Orthogonal skew-axis gearing

ABSTRACT

A skew-axis gearing which consists of a cylindrical worm and a flat worm wheel, which interengage beyond a plane passing through the wheel axis, normal; to the worm axis. To achieve elevated load capacity of this gearing in its action by either side of the worm threads, the profile of the latter is made curved.

United States Patent Georgiev et a1.

[4 1 Oct. 30, 1973 ORTHOGONAL SKEW-AXIS GEARiNG Inventors: AnatoiyKonstantinovich Georgiev,

ulitsa 9 Podlesnaya, 54, kv. 12; Veniamin losifovich Goldfarb, pereulokShkolny, 60, kv. 53, both of izhevsk, U..S.S.R.

Filed: Dec. 16, 1971 Appl. No.: 208,838

11.8. C1 74/425, 74/458, 74/459.5 lntrCl. F16h 1/16, F16h 55/04 Field ofSearch ..74/459.5, 425, 462,

References Cited UNITED STATES PATENTS 2/1972 Schrempp 74/425 X 7/1956Vaucher 74/462 X 2,752,751 4/1915 Weaver 74/459.5

Primary Examiner-Leonard H. Gerin Attorney-Eric H. Waters et al.

[57] ABSTRACT 3 Claims, 3 Drawing Figures li/ i /r -41 gm: m)

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The present invention relates to toothed gearings, and more specificallyto orthogonal skew axis gearings.

The present invention can be utilized in machinetools, motor cars,instruments and other technical fields, primarily there, where largeloads are to be transmitted within possibly small dimensions,particularly if low susceptibility of the gearing to assembly errors andits high operating smoothness are also desired.

Known in the art are orthogonal skew axis gearings, comprising acylindrical worm pinion of constant lead and a worm wheel made as a flatring with teeth formed on its face. In these gearings, said worm andworm wheel are disposed so, that the space within which they engage eachother (the zone of their engagement) is located aside of the planepassing through the axis of the worm wheel normally to the worm axis,and the profile of the side faces of the worm coils has a straight-lineshape (see, for example, British Pat. No. 940501, cl. F,2Q, published1963).

The following disadvantages are inherent in these gearings. i

To secure maximum contact strength, and therefore to provideclose-to-optimum values of the radii of curvature, of the worm coil orthread side surfaces facing the common interaxial perpendicular of thegearing (i.e., of the so-called front faces of the worm), as well as ofthe wheel teeth faces meshing therewith, quite a small value of theprofile angle of said front faces of the worm should be assumed. Butwith a straight-lined profile this turns out to be undesirable, first,due to the increased stress concentration at the base of the worm coilscaused by the fact, that the transition from their side faces to thededendum surface in this case becomes sharper, and second, because ofthe excess thinning, and hence, weakening, of the worm coil roots. Allthis involves reduced bending strength of the latter. That is whyproviding a close-to-optimum load capacity for load transmission by thefront faces of the worm and the corresponding wheel teeth faces turnsout to be difficult with such gearings.

. Besides that, to exclude undercuts and minimize the transition areason those side faces of the wheel teeth which engage the worm facesopposite to its front faces (i.e., the so-called rear faces of theworm), quite a large value of the profile angle of said rear faces ofthe worm has to be assumed in these gearings. But large values of thisprofile angle also involve large thrust forces tending to buckle theworm and the wheel, correct engagement thus being ultimately disturbed.What is more, increased values of the profile angle of said rear facesof the worm entail lower values of the reduced radii of curvature of theengaging faces of the worm and the wheel teeth, which tends to lessentheir contact strengthand the carrying capacity of the oil filmtherebetween.

This is why providing a close-to-optimum load capacity for loadtransmission by the rear faces of the worm and the corresponding facesof the wheel teeth is again difficult in such gearingst Y It is anobject of the present invention to eliminate the cited disadvantages.

An important object of the invention is to extend the load capacity ofthe gearing in working by either side of the worm coils or threads.

Another object of the invention is to increase the contact and thebending strength in working by the front faces of the worm.

One more object of the invention is to reducethe thrust forces acting inthe gearing, and to raise the carrying capacity of the oil film betweenthe rear face of the worm and the wheel tooth face engaging it, the sameundercutting expectancy of the latter being maintained.

It is also an object of the invention to ensure more complete adhesionof the worm faces to the wheel teeth faces engaging them.

Withthese and other objects in view, in an orthogonal skew axis gearing,comprising a worm wheel made as a flat ring with teeth formed on itsface, and. a cylindrical pinion worm meshing therewith and disposedbeyond the plane passing through the wheel axis normal to the worm axis,according to the invention, the profile of the side faces of the wormcoils is made curved, the sides facing the common interaxialperpendicular of the gearing having a concave profile, and the oppositesides having a convex profile. 7

Since the profile of the worm side faces is curved, angles a betweentangents to the profile in its points spaced varying distances from theworm axis, and the plane perpendicular to this axis turn out tobedifferent, whereas in the conventional gearing said angles a in saidpoints remain unchanged due tothe straight-lined profile of the wormcoils.

When angles a; in those profile points of the front face which lie onthe median cylinder of the worm, are for the conventional and theproposed gearingsequal, their angles a in the profile points lying onthe addendum cylinder of the worm are found to be unequal. And whereasin the conventional gearing Elf-"(1 in the proposed gearing theconcavityof the front face results in that angle a is quite small, less than saidangle or, Since a reduced angle a helps to increase contact strength,the concave profile of the front face is optimal from this standpoint.

Besides that, the concaveshape of the front face of the worm coil helps,first, to reduce stress concentrations at the coil base due to thetransition from the concave front face to the dedendum surface being nowsmoother, and second, to extend the thickness of the coil root, thusraising its bending strength.

Hence, making the front face of the coil concave increases the loadcapacity of the gearing when working with this face.

With equal angles a; in those points of the rear face profile, which lieon the median cylinder of the worm, in the conventional and the proposedgearings, and with accordingly equal values of thrust forces acting inthe gearingand determined by these angles, angles a, in the profilepoints lying on the addendum cylinder of the worm are unequal for thetwo gearings. And whereas in the conventional gearing 04501 in theproposed gearing the convexity of the rear" face results in that angle04.. is found to be more, than said angle 01 Since, from theundercutting conditions, it is just in the most distant point from theworm axis, that a larger angle is necessary, the convex profileof therear face is optimal from the standpoint of said condition.

On the other hand, with equal angles (1 and hence, equal expectancies ofundercutting the wheel teeth faces engaging the rear faces of the wormcoils, in

the conventional and the proposed gearings, angle a in the latter isless than angle owing to the convexity of the rear" face. This helps,first, to reduce the thrust forces acting in the gearing, and second, toraise the carrying capacity of the oil film enclosed between the convexrear face of the worm coil and the wheel tooth face interactingtherewith, and thus to increase the load capacity of the gearing whenworking by this side of the coil.

As we have disclosed from an analysis of the engagement conditions inthe proposed gearing, for a more effective increase of the load capacityof the gearing acting by the concave front face of the worm, theabove-said angles a, and a should advantageously be chosen within -20and 0-10, respectively, and it is expedient, that the centre C, ofcurvature of the concave profile of the front face in the point of itsintersection with the median cylinder of the worm be located outsidethis cylinder, and the radius 4), of curvature of this profile in saidpoint equal 0.5-2 diameters d of the median cylinder of the worm.

As to the convex rear face, to achieve a more effective increase of theload capacity of the gearing when acting by this side of the worm, theaforesaid angles a and a, should advisably be chosen within 20-35 and30-50, respectively, and it is expedient that the centre C of curvatureof the convex profile in the point of its intersection with the mediancylinder of the worm be located inside this cylinder, and radius ofcurvature of said profile in said point equal 0.5-1 .5 diameters d ofthe median cylinder of the worm.

For a better understanding of the invention following is a descriptionof a particular exemplary embodiment thereof with references to theappended drawings, wherein:

FIG. 1 shows the proposed gearing as viewed in the Y direction of theworm wheel axis;

FIG. 2 is a section through a worm coil of the gearing shown in FIG. 1,enlarged view;

FIG. 3 shows a speed reducer wherein the proposed gearing is employed.

.The gearing consists of a cylindrical worm 1 (FIG. 1) having an axis 2,and a worm wheel 3 with an axis 4 having the form of a flat ring withatoothed rim 5. Coils or threads 6 of worm l have a constant height hall across the worm length, which means that assumed as the dedendumsurface of coils 6 is a cylinder 7 equidistant from their addendumcylinder 8.

Worm 1 and wheel 3 are disposed so, that they engage each other beyondthe plane passing through axis 4 of wheel 3, which is normal to axis 2of worm 1.

Side faces 9 (FIG. 2) of coils 6 facing a common interaxialperpendicular 10 of the gearing (the so-called front faces) have aconcave profile, and opposite side faces 11 (the so-called rear faces)have a convex profile. v

The profile curves of coils 6 are smooth curves of any type, forexample, circular or elliptical arcs, sections of parabolas orsinusoids, etc.

The centre C, of curvature of the profile of the front" face 9 in point12 of its intersection with the generatrix of a median cylinder 13 ofcoils 6 of worm l is always located outside said cylinder 13,'and thecentre C, of curvature of the profile of the rear face 11 in point 14 ofits intersection with the generatrix of the median cylinder 13 of coils6 of worm 1 is always located inside said cylinder l3.

A tangent 15 to the profile of the front face 9 of the coil in point 12forms with a plane 16 perpendicular to axis 2 of worm 1 an angle or,whose value varies within 5 to 20, and a tangent 17 to the profile ofthe front" face 9 in point 18 of its intersection with the addendumcylinder 8 of coils 6 forms with plane 16 an angle a whose value variesbetween 0 and 10. Radius (1), of curvature of theprofile of the frontface 9 in point 12 equals 0.52.0 diameters d (FIG. 1) of the mediancylinder 13 of worm 1. The concave shape of the profile of the frontface 9 of coils 6, and the assumed ranges of values of angles 11,, a andradius (b, provided for an elevated contact and bending strength ofcoils 6, and hence, for an elevated load capacity of the gearing inworking with this side of the coil.

A tangent 19 (FIG. 2) to the profile of the rear face 11 of the coils inpoint 14 forms with the plane 16 perpendicular to axis 2 of worm 1 anangle 01 whose value varies between 20 and 35, while a tangent 20 to theprofile of the rear face 11 in point 21 of its intersection withtheaddendum cylinder 8 of coils 6 forms with-plane 16 an angle a, the valueof which varies within 30 to 50. The radius (b of curvature of theprofile of the rear face 1 1 in point 14 equals 0.5- 1.5 diameters d(FIG. 1) of the median cylinder 13 of worm l. The convex shape of theprofile of the rear" face 11 of coils 6, and the assumed ranges ofvalues of angles (1 a and of radius provide for an elevated loadcapacity of the gearing when working with this side of the coil.

For a more complete adhesion of the side faces of coils 6 of worm 1 tothe mating faces of teeth 22 of wheel 3, the axial lead I of coils 6should be calculated by formula where A is the centre distance, i.e.,the distance between points 0 and 0 of intersection of the commoninteraxial perpendicular 10 respectively with axis 2 of worm l and axis4 of the worm wheel 3, in mm;

n number of threads of worm l;-

i ratio of the number of teeth 22 of the worm wheel 3 to the number ofthreads n of worm 1, i.e. the reduction ratio of the gearing;

Z,,Z distances between the plane passing through the common interaxialperpendicular 10 normally to axis 2 of worm 1, and respectively the nearend face 23 and the far end face 24 of the meshing part of the worm, inmm;

R radius of the addendum cylinder 8 of coils 6 of worm 1, in mm.

The parameters of tooth 22 in the toothed rim 5 of wheel 3 aredetermined by the parameters of worm 1 and of the gearing as a whole.The gearing can be realized for reduction ratios of from 3 up to 450.

FIG. 3 shows an example of a particular use of the proposed gearing,namely a rear-axle speed reducer of a passenger car, wherein theabove-described gearing is employed as the axle drive. The use of thisgearing in said reducer permits increasing the longevity and reliabilityof the latter.

What we claim is:

1. An orthogonal non-intersecting axis gearing, comprising a flattoothed wheel and a cylindrical threaded worm the latter being displacedalong its axis from the axial plane of said wheel, which plane isperpendicular to said axis, the teeth of said wheel mating with theturns of the threads of said worm, the side faces of said thread turnsfacing the axis of said wheel and having in the normal section a concaveside profile, the other side faces of said thread turns having in thenormal section a convex side profile, said thread turns having aconstant axial pitch determined in accordance with the formula Rrepresents the radius of the addendum cylinder of said thread turns.

2., The gearing as defined in claim 1, wherein the tangent to saidconcave profile forms an angle within 5 and 20 with a plane which isperpendicular to said worm axis, at the points of intersection of saidconcave profile with the mid-cylinder of said worm; the tangent to saidconcave profile forms an angle within 0 and 10 with said perpendicularplane, at the points of intersection of said concave profile with theouter cylinder of said worm; the center of curvature of said concaveprofile is disposed beyond said mid-c ylinder at said points ofintersection with the same; and the radius of curvature of said concaveprofile is within 0.5d and 2d at the same points of intersection,wherein d, is the diameter of said mid-cylinder.

3. The gearing as defined in claim 1, wherein the tangent to said convexprofile forms an angle within 20 and 35 with a plane which isperpendicular to said worm axis, at the points of intersection of saidconvex profile with the mid-cylinder of said worm; the tangent to saidconvex profile forms an angle within 30 and 50 with'said perpendicularplane, at the points of intersection of said convex profile with theouter cylinder of said worm;'the center of curvature of said convexprofile is disposed inside said mid-cylinder at said points ofinter-section with the same; and the radius of curvature of said convexprofile is within 0.511 and 1.5d, at the same point of the intersection,wherein d is the diameter of said mid-cylinder.

1. An orthogonal slew-axis gearing, comprising a flat toothed wheel anda cylindrical threaded worm, the latter being displaced along its axisfrom the axial plane of said wheel, which plane is perpendicular to saidworm axis, the teeth of said wheel mating with the thread convolutionssaid worm, the side surfaces of said convolutions facing the axis ofsaid wheel and having in the normal section a concave side profile, theother side surfaces of said convolutions having in the normal section aconvex side profile, said convolutions having a constant axial leaddetermined in accordance with the formula
 2. The gearing as defined inclaim 1, wherein the tangent to said concave profile forms an anglewithin 5* and 20* with a plane which is perpendicular to said worm axis,at the points of intersection of said concave profile with themid-cylinder of said worm; the tangent to said concave profile forms anangle within 0* and 10* with said perpendicular plane, at the points ofintersection of said concave profile with the outer cylinder of saidworm; the center of curvature of said concave profile is disposed beyondsaid mid-cylinder at said points of intersection with the same; and theradius of curvature of said concave profile is within 0.5d1 and 2d1 atthe same points of intersection, wherein d1 is the diameter of saidmid-cylinder.
 3. The gearing as defined in claim 1, wherein the tangentto said convex profile forms an angle within 20* and 35* with a planewhich is perpendicular to said worm axis, at the points of intersectionof said convex profile with the mid-cylinder of said worm; the tangentto said convex profile forms an angle within 30* and 50* with saidperpendicular plane, at the points of intersection of said convexprofile with the outer cylinder of said worm; the center of curvature ofsaid convex profile is disposed inside said mid-cylinder at said pointsof intersection with the same; and the radius of curvature of saidconvex profile is within 0.5d1 and 1.5d1 at the same points ofintersection, wherein d1 is the diameter of said mid-cylinder.